To measure primary production of algae in a stream, you place two sealed chamber

Question

To measure primary production of algae in a stream, you place two sealed chambers in the stream, each enclosing the sediments as well as the water above them. One chamber is covered with black tape (blocking all light) while the other is transparent to light.

You measure dissolved oxygen (DO) before and after a 24-hour incubation. DO in the light chamber increased by 1.5 g/m2 while DO in the dark chamber decreased by 2.0 g/m2.

(Hint: You have all the information you need to answer the following 3 questions—you do not need initial and final DO values. Think carefully about what is actually being measured in each of the two chambers!)

Q2.30. What is the estimated ecosystem respiration (Re) for the stream?

answer __ gO2 m-2 day-1

Explanation / Answer

Answer: Respiration is decrease in DO per day and respiration rate is decrease in DO per hour. Therefore, estimated ecosystem respiration (Re) is 2.0 gO2 m-2 day-1. In the transparent chamber both photosynthesis and respiration will occur, whereas in black tape covered chamber only respiration will occur. Respiration leads to decrease in DO. Thus, respiration is measured by decrease in DO.

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